1. Field of the Invention
This invention relates to a method for separating pieces from a super hard material plate by partially cutting the plate with a laser along the top of the plate and then subsequently cleaving the uncut portion by applying pressure to the plate along the line of the cut. More particularly, the invention relates to the separation of diamond devices, especially heat sinks for semiconductor devices, from diamond plates.
2. Description of the Prior Art
Lasers have been used to cut, scribe and etch various materials. U.S. Pat. No. 5,168,143 describes the cutting of metal plates with a laser. The laser cutting of glass is described in U.S. Pat. Nos. 4,467,168 and 4,682,003. The cutting and machining of ceramics with a laser are described in U.S. Pat. No. 4,169,976 and 5,138,130.
Lasers have also been effective in the cutting or scribing of super hard materials such as diamonds. U.S. Pat. No. 4,467,172 and 5,149,938 disclose the inscribing of diamonds with lasers. U.S. Pat. No. 5,012,067 discloses a method for cutting synthetic diamond workpieces.
Its hardness, thermal and electrical properties have made diamond useful in a variety of industrial applications. The high heat conductance and excellent electrical insulation properties of natural and synthetic diamond make it ideal for use as heat sinks for electronic components.
Presently the manufacture of diamond based heat sinks as well as other diamond based devices involves forming a plurality of the devices on a synthetic diamond plate and separating the individual devices from the plate. The synthetic diamond may be formed by a high pressure/high temperature method (HP/HT) or by a low pressure chemical vapor deposition (CVD) method. The individual devices are separated from the plate by cutting through the entire thickness of the plate with a laser.
This method of separating the devices from the plate presents two problems. First, as the diamond is cut by the laser graphite deposits are left on the walls of the cut. Graphite is an electrical conductor which when deposited on the cut walls tends to induce electrical conductivity between features of the device which are designed to be electrically isolated. Additionally, there may occur electrical conductance between the top and bottom surfaces of the device. Both situations lead to an increase in device failure because of the difficulty in removing the graphite.
Second, the devices are handled manually after cutting because of the difficulty of automating the cleaning and processing of the individual devices. This leads to a process that is slow, inefficient, and labor intensive. Also, additional higher yield loss occurs due to damage from increased handling.
Therefore, it is desirable to provide a method of separating pieces from diamond and other super hard material plates without compromising the inherent properties of the material. Moreover, a method of separating is desired which allows automation of the entire manufacturing process.
U.S. Pat. No. 4,248,369 discloses a method for laser cutting of ceramic tubing. The laser is use to drill holes at intervals around the circumference of the tubing to create a line of weakness. The tubing is then broken along the line of weakness.
U.S. Pat. No. 4,224,101 discloses a method of manufacturing semiconductor devices by partially laser cutting a disc of semiconductor material, upon which is disposed a plurality of devices. The debris from the cut is removed by preferential etching and the devices are separated from the disc.